The present invention relates to a fuel evaporator for use in a fuel entry system of an internal combustion engine.
Ceramics containing barium titanate as a main ingredient, for example, have a positive temperature coefficient of resistance and the resistance thereof is suddenly increased at a specific temperature. The temperature at which the electric resistance of the ceramics is suddenly increased (that is Curie temperature) is ranged from 120.degree. C. to 150.degree. C. due to the difference of the material of the ceramics. Under the Curie temperature, a large amount of electric current flows. And the temperature of the ceramics rises up to the Curie temperature rapidly. Then, over the Curie temperature, the electric resistance is remarkably increased so that only a small amount of electric current flows. Thus, the ceramics keep the temperature thereof at about the Curie temperature thereof.
A heater using the above described ceramics (PTC heater) can be applied to an internal combustion engine as a fuel evaporator for heating and evaporating fuel droplets.
Conventionally, engine cooling water and exhaust gas have been employed to heat and evaporate the fuel droplets.
However, at a cold starting time of the engine, the temperature thereof does not rise rapidly so that the fuel droplets were not heated nor evaporated sufficiently.
In contrast, PTC heater reaches the Curie temperature instantly when electrified. Therefore, PTC heater is preferable as a fuel evaporator of the engine.
However, there is a problem when the PTC heater is used as the fuel evaporator. Namely, the PTC heater consumes considerably large amount of electric power so that the voltage of the battery drops to lower the capacity of other electric apparatus connected thereto.
In particular, at an engine starting time, the electric power required to operate a starting motor cannot be sufficiently obtained so that the starting condition of the engine is not good.
Accordingly, one object of the present invention is to provide a fuel evaporator having a PTC heater, which can evaporate fuel droplets within a fuel entry system by only a small amount of electric power with high efficiency.
Another object of the present invention is to provide a fuel evaporator having a PTC heater which controls the electric current in response to the driving condition of the engine.
Still another object of the present invention is to provide a fuel evaporator having a PTC heater, which does not prevent the engine from starting in a good condition.